tendineæ_, connect the edges and apices of these valves with
column-like elevations of the fleshy substance of the walls of the
ventricles, called _columnæ carneæ_.

[Illustration: Fig. 41.
1. The descending vena cava. 2.
The ascending vena cava. 3. The
right auricle. 4. The opening between
the right auricle and the right
ventricle. 5. The right ventricle. 6.
The tricuspid valves. 7. The pulmonary
artery. 8, 8. The branches
of the pulmonary artery which pass
to the right and the left lung. 9. The
semilunar valves of the pulmonary
artery. 10. The septum between the
two ventricles of the heart. 11, 11.
The pulmonary veins. 12. The left
auricle. 13. The opening between
the left auricle and ventricle. 14.
The left ventricle. 15. The mitral
valves. 16, 16. The aorta. 17. The
semilunar valves of the aorta.]

The valves are so arranged that they present no obstacle to the free
flow of blood from the auricles into the ventricles, but if any is
forced the other way, it gets between the valve and the wall of the
heart, and drives the valve backwards and upwards, thus forming a
transverse partition between the auricle and ventricle, through which no
fluid can pass.